A gland found near the rectum of elasmobranch fishes that removes excess sodium chloride (NaCl) from the blood. It consists of numerous blind-ending tubules surrounded by blood capillaries; the tubules drain into a duct that opens into the intestine. Sodium-potassium pumps in the cells lining the tubules create a concentration gradient of Na⁺ ions across the serosal (blood) surface of the tubules, which in turn drives a cotransport system that moves chloride ions (Cl^–) from the blood into the tubule cells. The resulting raised intracellular concentration of Cl^– ions causes them to diffuse from the tubule cells into the duct lumen, and the consequent electrochemical gradient causes Na⁺ ions to follow between the cells. Water also diffuses passively into the lumen, creating a solution that has the same osmolarity as the blood but containing a much higher concentration of NaCl. See also salt gland.